Robust flow-through platform for organic contaminants removal

ABSTRACT

Disclosed is an electro-Fenton-like (EFL) platform wherein an electrochemically produced acidic environment supports heterogeneous Fenton-like reaction for high throughput water treatment. The platform enables treatment of contaminated water.

RELATED APPLICATION

This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/939,871, filed Nov. 25, 2019.

GOVERNMENT SUPPORT

This invention was made with government support under Grant Number P42ES017198 awarded by the National Institutes of Health. The government has certain rights in the invention.

BACKGROUND

Various toxic organic compounds in the environment have produced considerable threats to human health and ecosystem. While efficient in providing clean drinking water with improved quality, many advanced water treatment facilities are flawed by high capital costs and remain as the principal barrier for implementation in developing countries (Lu et al. 2018). The classic Fenton process, which transforms hydrogen peroxide (H₂O₂) into hydroxyl radicals (HO.) under the ferrous ions (Fe²⁺) catalysis, is an affordable and proven water treatment technique (Wardman et al. 2018). HO. is the second most oxidative species with a redox potential of 2.73 V (vs NHE) after fluorine in nature (Wardman et al. 2018), and could non-selectively destroy recalcitrant and toxic organic contaminants in water (Babuponnusami et al. 2014; Pignatello et al. 2006). By coupling with other water treatment units, such as coagulation, membrane filtration, or microbial degradation, the Fenton process can be adapted for various water bodies' treatments (Feng et al. 2010; Wu et al. 2011; Ganiyu et al. 2015). Fruitful progresses have been achieved to date in Fenton chemistry for water treatment (Herney-Ramirez et al. 2010; Pouran et al. 2015; Bokare et al. 2014; Brillas et al. 2009; Ganiyu et al. 2018). In particular, in situ synthesis of H₂O₂ from H₂ and O₂ under noble metal catalysis (Yi et al. 2016), and H⁺ and O₂ under photochemical (Moon et al. 2017), or electrochemical catalysis (Bolobajev et al. 2014) is a sustainable route to reduce the chemical cost. However, formation of the ferric sludge continues to be a challenge limiting implementation of the Fenton process. The sludge is formed when water pH is improved to around neutral after oxidation, and its toxicity stems from the adsorbed residual compounds in treated water (Bolobajev et al. 2014). Treatment of the ferric sludge requires substantial chemical and manpower costs—10% to 50% of overall operating costs in a water treatment plant (Pilego et al. 2012; Neyens et al. 2003).

Heterogeneous solid catalysts could potentially overcome the drawback of ferric sludge formation. Naturally occurring clays/minerals as well as transition metal-centered designer composites have been extensively explored as Fenton-like catalyst (Herney-Ramirez et al. 2012; Garrido-Ramirez et al. 2010; Cheng et al. 2018; Munos et al. 2015; Pouran et al. 2014). These catalysts have noteworthy structural elegance in the unique coordination environment of their metal cores, which stabilizes the metal-H₂O₂ complex transition state and facilitates the electron transfer inter se (Sun et al. 2018). Furthermore, the turnover of metal atoms on the catalyst surface occurs via a peroxidase-mimicking mechanism (Gao et al. 2007), akin to the Haber-Weiss reaction of homogeneous Fenton chemistry (Koppenol et al. 2001). The pH-dependence of heterogeneous Fenton-like catalysts is generally less strict than that of iron ions, the latter of which is most effective in pH 2.8-3.5 (Cheng et al. 2018). Nevertheless, most canonical Fenton-like catalysts favor acidic pH 3-5 (Table 1), and catalysts turnover frequency (TOF) can be reduced by up to 100 folds under neutral condition (Liu et al. 2011; André et al. 2011). This is due to surface metal-OH complexes forming at higher pH values and repelling H₂O₂ away from the exposed active sites. However, pH regulation of near-neutral drinking water bodies is challenging, especially if the water contains high carbonate alkalinity; furthermore, acidification of contaminated groundwater for in situ water treatment could release undesired metal ions from aquifers (Keith et al. 2001; Nordstrom et al. 1999). These concerns severely compromise the potential use of heterogeneous Fenton-like catalysts in the water treatment industry.

Flow electrochemistry holds great potential for automatic pH regulation to support water treatment, wherein OH⁻ and H⁺ generated from the cathode and anode, respectively, are redistributed based on ion migration, dispersion, and hydraulic flux (Acar et al. 2011).

SUMMARY OF INVENTION

One aspect of the present invention provides a process for treating contaminated water, comprising contacting said contaminated water with hydrogen peroxide in the presence of an iron oxychloride catalyst, wherein the process occurs in the absence of an acid.

Another aspect of the invention provides a process for treating contaminated water, comprising: (i) adding hydrogen peroxide to the contaminated water; (ii) providing an influent stream of the contaminated water into a chamber comprising an upstream anode, a downstream cathode, and an iron oxychloride catalyst between the anode and cathode; (iii) applying an electric current to the chamber to provide an acidic environment in the chamber so as to thereby treat the contaminated water in the chamber; and (iv) collecting an effluent stream of the treated water exiting the chamber.

Also provided herein is a process for treating contaminated water, comprising contacting said contaminated water with hydrogen peroxide in the presence of an iron oxychloride catalyst, wherein the process occurs in the absence of an acid, wherein the treating comprises removal of bisphenol A from the water.

Also provided herein is a process for treating contaminated water, comprising: (i) adding hydrogen peroxide to the contaminated water; (ii) providing an influent stream of the contaminated water into a chamber comprising an upstream anode, a downstream cathode, and an iron oxychloride catalyst between the anode and cathode; (ii) applying an electric current to the chamber to provide an acidic environment in the chamber so as to thereby treat the contaminated water in the chamber; and (iv) collecting an effluent stream of the treated water exiting the chamber, wherein the treating comprises removal of bisphenol A from the water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A: Electrolytically localized acid-compartment process-based flow-through water treatment platform (Ella process). Schematic representation of the flow-through platform. Placement of an anode upstream of a cathode produces an acid front, which promotes the activity of immobilized Fenton-like catalyst. The H₂O₂ is in situ transformed into HO. radical under catalysis, leading to oxidative mineralization of organic contaminant into CO₂ and H₂O. Bisphenol A (BPA) is used as a target compound for illustration purpose.

FIG. 1B: Automatic pH regulation by the Ella process. Left panel depicts the setup configuration, and right panel indicates the pH variation profile along the column axis as the applied electric current was turned off and on. Arrows indicate flow direction. “+” and “−” denote anode and cathode, respectively.

FIG. 2A: Characterizations of synthesized FeOCl nanosheet catalyst: TEM image.

FIG. 2B: Characterizations of synthesized FeOCl nanosheet catalyst: HRTEM image.

FIG. 2C: Characterizations of synthesized FeOCl nanosheet catalyst: Element mapping images.

FIG. 2D: Characterizations of synthesized FeOCl nanosheet catalyst: Element ratio measurement from EDX analysis.

FIG. 3A: XPS characterization of FeOCl sample: Survey spectrum.

FIG. 3B: XPS characterization of FeOCl sample: Fe 2p.

FIG. 3C: XPS characterization of FeOCl sample: O 1s.

FIG. 3D: XPS characterization of FeOCl sample: Cl 2p.

FIG. 4A: Activity of synthesized FeOCl:BPA degradation by FeOCl/H₂O₂ reaction.

FIG. 4B: Activity of synthesized FeOCl: Quantification of generated HO. radical by FeOCl/H₂O₂ reaction at different pH.

FIG. 5 : Peroxidase-like catalysis mechanism of FeOCl/H₂O₂ reaction.

FIG. 6 : Reaction energy in step 1 (top) and step 2 (bottom) based on DFT calculation. Step 1: Fe^(III)OCl is at first reduced by H₂O₂ into Fe^(II)OCl, and Step 2: the derived Fe^(II)OCl then decomposes H₂O₂ into HO. radical via homolytic cleavage.

FIG. 7A: BPA removal by EFL platform loading unimmobilized FeOCl: Illustration of reactor components.

FIG. 7B: BPA removal by EFL platform loading unimmobilized FeOCl: BPA removals from each sampling port as the electric current was turned on and off.

FIG. 8 : Stability test of BPA removal by reactor loading unimmobilized FeOCl (shown in FIG. 7A) for 8 h.

FIG. 9A: Immobilization of FeOCl on alginate hydrogel: Illustration of immobilization strategy.

FIG. 9B: Immobilization of FeOCl on alginate hydrogel: SEM images.

FIG. 9C: Immobilization of FeOCl on alginate hydrogel: XRD characterizations.

FIG. 10A: Activity of synthesized FeOCl: BPA degradation by FeOCl/H₂O₂ reaction.

FIG. 10B: Activity of synthesized FeOCl: Quantification of generated HO. radical by FeOCl/H₂O₂ reaction at different pH.

FIG. 11A: BPA removal by EFL platform loading FeOCl/alginate catalyst composite: Illustration of reactor components. The 4.5 g (dry weight) as-prepared FeOCl/alginate was filled in between the cathode and anode, and all other spaces were filled with glass beads to reduce hydrodynamic perturbation. The pore volume of our reactor between cathode and anode was 60 mL. Typically, a neutral solution containing 10 mM H₂O₂, 10 μM BPA, and 5 mM Na₂SO₄ as electrolyte was pumped up into the vertically aligned reactor at a rate of 3 mL/min. A steady-state acidic-compartment was formed between the cathode and anode under a current of 40 mA after 60 min, and FeOCl/alginate catalyzed H₂O₂ decomposition for BPA removals was tested.

FIG. 11B: BPA removal by EFL platform loading FeOCl/alginate catalyst composite: BPA removals from each sampling port as the electric current was turned on and off.

FIG. 12 : BPA removal under different flow rate by EFL platform loading FeOCl/alginate catalyst composite (as shown in FIG. 11A).

FIG. 13A: Immobilization of FeOCl onto γ-Al₂O₃ support. Illustration of melt infiltration strategy.

FIG. 13B: SEM image of γ-Al₂O₃. Scale bars indicate 1 μm.

FIG. 13C: SEM image of FeOCl. Scale bars indicate 1 μm.

FIG. 13D: SEM image of FeOCl/Al₂O₃. Scale bars indicate 1 μm.

FIG. 13E: EDX element mapping and analysis of FeOCl/Al₂O₃. Scale bars indicate 1 μm.

FIG. 13F: XRD pattern of FeOCl/Al₂O₃.

FIG. 13G: Fe 2p deconvolution spectra of XPS analysis. Scale bars indicate 1 μm.

FIG. 14A: XPS characterization of γ-Al₂O₃: Survey spectrum. The observed Al—O—H bond was due to chemisorbed moisture on γ-Al₂O₃ surface.

FIG. 14B: XPS characterization of γ-Al₂O₃: Al 2p. The observed Al—O—H bond was due to chemisorbed moisture on γ-Al₂O₃ surface.

FIG. 14C: XPS characterization of γ-Al₂O₃: O 1s. The observed Al—O—H bond was due to chemisorbed moisture on γ-Al₂O₃ surface.

FIG. 15A: XPS characterization of FeOCl/Al₂O₃: Survey spectrum. Fe 2p deconvolution spectra are shown in FIG. 13G in the main text.

FIG. 15B: XPS characterization of FeOCl/Al₂O₃: Al 2p. Fe 2p deconvolution spectra are shown in FIG. 13G in the main text.

FIG. 15C: XPS characterization of FeOCl/Al₂O₃: Cl 1s. Fe 2p deconvolution spectra are shown in FIG. 13G in the main text.

FIG. 15D: XPS characterization of FeOCl/Al₂O₃: O 1s. Fe 2p deconvolution spectra are shown in FIG. 13G in the main text.

FIG. 16A: Catalytic activity of FeOCl/Al₂O₃ composite. BPA degradation by FeOCl/Al₂O₃ and H₂O₂ reaction and controls. Reactions were performed at pH 3.

FIG. 16B: Catalytic activity of FeOCl/Al₂O₃ composite. Quantification of generated HO. radical by FeOCl/Al₂O₃ and H₂O₂ reaction at different pH after reaction for 30 min. Inset shows the stoichiometric oxidation of benzoic acid for HO. radical yield determination.

FIG. 17A: Illustration of column device components of electro-Fenton-like platform. Arrows indicate flow direction. “+” and “−” denote anode and cathode, respectively.

FIG. 17B: BPA removals from each sampling port of electro-Fenton-like platform.

FIG. 17C: Quantification of generated HO. radical by electro-Fenton-like platform as the electric current was turned off and on;

FIG. 17D: Stability test of electro-Fenton-like platform.

FIG. 17E: Tolerance of flow rate of electro-Fenton-like platform. Influent flow rate was subjected to change.

FIG. 17F: Electricity responsiveness assay of the electro-Fenton-like platform.

FIG. 18 : Control experiments of column reaction. BPA removal by the EFL water treatment platform with 1). Both FeOCl/Al₂O₃ and H₂O₂, 2). Only FeOCl/Al₂O₃, 3). Only H₂O₂, and 4). FeOCl/Al₂O₃, H₂O₂, and ethanol. Reaction conditions: 100 mA electric current, 15 mL/min flow rate, 10 mM H₂O₂, 5 mM Na₂SO₄ electrolyte, pH 7. When FeOCl/Al₂O₃ was not used, silica sand particles were filled into the catalyst zone instead. 10 mM ethanol was used as HO. radical quencher.

FIG. 19 : Degradation of recalcitrant organic contaminants by the developed electro-Fenton-like water treatment platform. Initial concentration of these compounds was 10 μM.

FIG. 20A: Robustness of electro-Fenton-like platform against complex water chemistry. Acidic pH produced by Ella process. Influents were adjusted to different initial pH. Ella pH denotes the average of solution pHs from two middle sampling ports.

FIG. 20B: BPA removals when the electric current was turned off and on BPA removals when the electric current was turned off and on. Influents were adjusted to different initial pH. Ella pH denotes the average of solution pHs from two middle sampling ports.

FIG. 20C: Robustness of electro-Fenton-like platform against complex water chemistry. (Acidic pH produced by Ella process. Sodium carbonate was added to influents for synthetic alkalinity and influents were maintained neutral.

FIG. 20D: BPA removals when the electric current was turned off and on BPA removals when the electric current was turned off and on. Sodium carbonate was added to influents for synthetic alkalinity and influents were maintained neutral.

FIG. 21 : BPA removals when the electric current was turned off and on BPA removals when the electric current was turned off and on. Sodium carbonate was added to influents for synthetic alkalinity and influents were maintained neutral.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a Fenton-like water treatment process that bypasses the need of acid and generation of iron sludge precipitate, and makes the process more widely applicable to various conditions. This Fenton-like process is greener and more cost-effective than current methods.

Toxic organic compounds in water severely threaten drinking water safety, and require effective pretreatment. Hydroxyl radical produced by Fenton process (Fe²⁺/H₂O₂) can non-selectively destroy organic contaminants based on its strong oxidation potential. An upgraded reaction utilizing heterogeneous solid catalysts, called Fenton-like process, was recently adopted to overcome ferric sludge precipitation of Fenton process. However, most heterogeneous Fenton-like catalysts operate optimally at pH 3-5, which acidity is challenging to create in near-neutral water bodies. The Ella process produced by electrochemical water splitting under flow-through conditions to facilitate the heterogeneous Fenton-like reaction. This Ella process boosted the activity of an immobilized iron oxychloride catalyst by over ten-fold in terms of hydroxyl radical yield, leading to near 100% destruction of various organic pollutants under high-throughput treatments. The robust performance in complex water bodies further highlights the promise of this scalable platform.

The Ella process uses a high-performance iron oxychloride nanocatalyst instead of free iron ion, an acid compartment induced by electrolysis instead of addition of acid. The immobilized iron oxychloride nanocatalyst is confined to the acid compartment.

The advantages of the Ella process include the ability to treat water contaminants in neutral solution without the addition of acids, prevent the generation of iron sludge waste as a secondary pollutant, and a simple operating procedure (i.e. by simply switching the electricity from the power supply). Also, the preparation of catalysts and induction of acid compartment are more cost-effective than previous homogeneous Fenton process, and contaminated water can be treated with high efficiency and robustness against complex water chemistry. Avoidance of secondary pollutants, and treatment of secondary contamination also provides a cost reduction.

The Ella process can be used in an advanced oxidation process in water treatment plants to replace the currently prevalent homogeneous Fenton process. The process can be used for water decontamination and disinfection of most surface water and groundwater as well as complex water bodies, such as industrial wastewater.

Definitions

The term “contaminated water” as used herein refers to water containing one or more contaminants or pollutants. The contaminants or pollutants include, but are not limited to, organic contaminants or pollutants. The organic contaminants or pollutants include but are not limited to, drugs (e.g., ibuprofen and carbamazepine), drug precursors (e.g., 4-chlorophenol and 4-nitrophenol), plastic precursors (e.g., bisphenol A), herbicides (e.g., atrazine), pesticides, or recalcitrant dyes (e.g., rhodamine B, reactive blue 19, and orange II).

The term “iron oxychloride catalyst” as used herein refers to a FeOCl catalyst which is effective in catalyzing the production of hydroxyl radical (HO′) from hydrogen peroxide (H₂O₂). In the first step of the process of producing hydroxyl radical, Fe^(III)OCl is reduced by H₂O₂ into Fe^(II)OCl, and in the second step the derived Fe^(II)OCl then decomposes H₂O₂ into HO. radical via homolytic cleavage.

Although this invention demonstrates that iron oxychloride as a catalyst is powerful to treat pollutants, any other active Fenton-like catalyst can be used herein for water treatment.

In certain embodiments, any active Fe-based Fenton-like catalyst can be used herein for water treatment.

In certain embodiments, any active Mn-, Cu-, Co-, or Ni,-based Fenton-like catalyst can be used herein for water treatment.

Any catalyst listed in below Table 1, e.g., Fe₃O₄, KFePW₁₂O₄₀, H₃PW₁₂O₄₀, FA-Fe₂SiW₁₀, V₂O₅, Nanoceria, Co₃O₄, MnFe₂O₄, ferrocene, Ag₃PO₄, nanodiamond—gold nanocomposites, MOF-88, nitrogen-doped graphene quantum dots, Carboxyl-modified graphene oxide, H@M, Cubic Pt nanocrystal, Rh NS, MoS₂ NS, MoSe₂ NS, WΩ NS, WSe₂ NS, ZIF-67, Cu-MOF, Fe₂O₃, 2LFh, PdCu, Co₉S₈, Cu(OH)₂ SC, Ru frame, FePt—Au HNP, PtAg—MoS₂, PtPd NP, Cu-hemin, PS@Au@PB, and Cu NC, is useful in the disclosed treatment process.

Additional catalysts are also useful in the disclosed treatment process including ferrihydrites (e.g., 8% Ag/AgBr/Fh and 6% Ag/AgCl/Fh), ferrites (e.g., ZnFe₂O₄), pillared clays (e.g., Al—Fe smectite pillared clay), layered double hydroxides (e.g., CuNiFe LDH), Fe-Perovskites (e.g., LaCuxFe_(t-x)O_(3-δ) (x=0.5)), graphene related materials (e.g., Fe₃O₄—Mn₃O₄/reduced graphene oxide), g-C₃N₄ composites (e.g., Fe-g-C₃N₄/graphitised mesoporous carbon and 5% Fe-doped g-C₃N₄), metal-organic frameworks (MOFs) and composites (e.g., TiO₂ @NH₂-MIL88B-Fe), and zero-valent iron (ZVI) based catalysts (e.g., nano-ZVI@kaolinite) (see Thomas et al. 2021).

In certain embodiments, a Fenton-like catalyst which is active at acidic pH can be used for water treatment. In some embodiments, a Fenton-like catalyst which is active at pH 2-4 can be used for water treatment.

In certain embodiments, the Fenton-like catalyst is immobilized. In some embodiments, the Fenton-like catalyst is immobilized onto a support. The immobilization method is not limited to the disclosed methods, e.g., melt infiltration method. For example, ball milling can also be used as the immobilization method.

TABLE 1 Summary of heterogeneous Fenton-like catalysts owning peroxidase-mimicking functions in literature. Optimum Synthesis Catalyst Activity pH method Reference Horseradish TMB: K_(m) = 0.434 mM, 4 Genetically Gao et peroxidase V_(max) = 10 × 10⁻⁸ M s⁻¹, encoded al. 2007 (HRP) k_(cat) = 0.4 × 10⁴ s⁻¹; H₂O₂: K_(m) = 3.7 mM, V_(max) = 8.71 × 10⁻⁸ M s⁻¹, k_(cat) = 0.348 × 10³ s⁻¹; Fe₃O₄ TMB: K_(m) = 0.098 mM, 3.5 Solvothermal Gao et k_(cat) = 3.02 × 10⁴ s⁻¹; method, co- al. 2007; H₂O₂: K_(m) = 154 mM, precipitation Deng et k_(cat) = 8.58 × 10⁴ s⁻¹ method al. 2005; Ma et al. 2004; KFePW₁₂O₄₀ TMB: K_(m) = 0.346 mM, 4.5 1) Synthesis Zeb et V_(max) = 3.7 × 10⁻⁸ M s⁻¹; of K₃PW₁₂O₄₀ al. 2018 H₂O₂: K_(m) = 165 mM, through V_(max) = 6.9 × 10⁻⁸ M s⁻¹ hydrothermal treatment of KCl and H₃[PW₁₂O₄₀]; 2) iron ion exchange with K⁺ H₃PW₁₂O₄₀ TMB: K_(m) = 0.11 mM, 3 N.A. Wang et V_(max) = 43.1 × 10⁻⁸ M s⁻¹; al. 2012 H₂O₂: K_(m) = 15.89 mM, V_(max) = 42400 × 10⁻⁸ M s⁻¹ FA—Fe₂SiW₁₀ H₂O₂: K_(m) = 0.014 mM, 4 Co-precipitation Sun et V_(max) = 14.24 × 10⁻⁸ M s⁻¹ method al. 2013 V₂O₅ TMB: K_(m) = 0.165 mM, 4 Hydrothermal Qu et al. V_(max) = 2.4 × 10⁻⁸ M s⁻¹; method 2014 H₂O₂: K_(m) = 0.058 mM, V_(max) = 1.4 × 10⁻⁸ M s⁻¹ Nanoceria TMB: K_(m) = 3.8 mM, V_(max) = 4 Solution reaction Asati et 70 × 10⁻⁸ M s⁻¹ at room al. 2009 temperature CO₃O₄ TMB: K_(m) = 0.037 mM, 6 Heating and Mu et al. V_(max) = 6.27 × 10⁻⁸ M s⁻¹; precipitation 2012 H₂O₂: K_(m) = 140 mM, V_(max) = 12.1 × 10⁻⁸ M s⁻¹ MnFe₂O₄ TMB: K_(m) = 0.112-0.543 3.5 Heating and Peng et mM, V_(max) = (3.53-69.8) × precipitation al. 2015 10⁻⁴ M s⁻¹; H₂O₂: K_(m) = 0.00146-0.0964 mM, V_(max) = (5.15-71.5) × 10⁻⁴ M s⁻¹ Ferrocene TMB: K_(m) = 0.13 mM, V_(max) = 3 Commercially Wang et 4.79 × 10⁻⁹ M s⁻¹, k_(cat) = available al. 2018 4.79 × 10⁻³ s⁻¹; H₂O₂: K_(m) = 50.08 mM, V_(max) = 9.77 × 10⁻⁹ M s⁻¹, k_(cat) = 9.77 × 10⁻³ s⁻¹; Ag₃PO₄ TMB: K_(m) = 0.327 mM, 2.5 Solution reaction Liu et V_(max) = 2.01 × 10⁻⁸ M s⁻¹; at room al. 2014 H₂O₂: K_(m) = 0.216 mM, temperature V_(max) = 1.27 × 10⁻⁸ M s⁻¹ Nanodiamond- OPD: K_(m) = 6.4-48.7 mM, N.A. Solution reduction Kim et g old k_(cat) = 290.4-319.3 mM s⁻¹ mg⁻²; and heating al. 2016 nanocomposites H₂O₂: K_(m) = 89.7-208.7 mM, k_(cat) = 377.6-565.6 mM s⁻¹ mg⁻²; MOF-88 TMB: K_(m) = 0.0796 mM, 3 Heating and Zheng et V_(max) = 3.12 × 10⁻⁸ M s⁻¹; precipitation al. 2016 H₂O₂: K_(m) = 1.06 mM, V_(max) = 1.39 × 10⁻⁸ M s⁻¹ Nitrogen- TMB: = 11.19 mM, V_(max) = 3 Acid treatment of Lin et doped 0.38 × 10⁻⁸ M s⁻¹; graphene oxide al. 2015 graphene H₂O₂: K_(m) = 0.1 mM, V_(max) = quantum dots 0.14 × 10⁻⁸ M s⁻¹ Carboxyl- TMB: K_(m) = 0.0237 mM, 4 KMnO₄ Song et modified V_(max) = 3.45 × 10⁻⁸ M s⁻¹; oxidation of al. 2010 graphene H₂O₂: K_(m) = 3.99 mM, graphene oxide oxide V_(max) = 3.85 × 10⁻⁸ M s⁻¹ H@M TMB: K_(m) = 10.9 mM, 5 Impregnation of Qin et V_(max) = 8.98 × 10⁻⁸ M s⁻¹; hemin into MOF al. 2013 H₂O₂: K_(m) = 0.068 mM, V_(max) = 6.07 × 10⁻⁸ M s⁻¹ Cubic Pt N.A. 3.4 Solution reduction Ma et al. nanocrystal and heating 2011 Rh NS TMB: K_(m) = 0.264 mM, 4 Solution reduction Cai et V_(max) = 12.56 × 10⁻⁸ M s⁻¹, and heating al. 20118 k_(cat) = 8.2 × 10⁴ s⁻¹; H₂O₂: K_(m) = 4.51 mM, V_(max) = 68.09 × 10⁻⁸ M s⁻¹, k_(cat) = 44.5 × 10⁴ s⁻¹; MoS₂ NS TMB: K_(m) = 0.525 mM,   2-7.5 Solution-based Lin, Zhong V_(max) = 5.16 × 10⁻⁸ M s⁻¹; exfoliation et al. 2014 H₂O₂: K_(m) = 0.0116 mM, V_(max) = 4.29 × 10⁻⁸ M s⁻¹ MoSe₂ NS TMB: K_(m) = 0.014 mM, 3.5 Liquid exfoliation Wu et al. V_(max) = 0.56 × 10⁻⁸ M s⁻¹; method 2018 H₂O₂: K_(m) = 0.155 mM, V_(max) = 0.99 × 10⁻⁸ M s⁻¹ WS₂ NS TMB: K_(m) = 1.83 mM, V_(max) = 2-7 Commercially Lin et 4.31 × 10⁻⁸ M s⁻¹; available al. 2014 H₂O₂: K_(m) = 0.24 mM, V_(max) = 4.52 × 10⁻⁸ M s⁻¹ WSe₂ NS TMB: K_(m) = 0.0433 mM, 3.5 Liquid exfoliation Chen, Wu V_(max) = 1.43 × 10⁻⁸ M s⁻¹; method et al. 2018 H₂O₂: K_(m) = 19.53 mM, V_(max) = 2.22 × 10⁻⁸ M s⁻¹ ZIF-67 TMB: K_(m) = 13.69 mM, <4 Heating and Wang, Xu V_(max) = 0.35 × 10⁻⁸ M s⁻¹; precipitation et al. 2018 H₂O₂: K_(m) = 3.52 mM, V_(max) = 0.28 × 10⁻⁸ M s⁻¹ Cu-MOF TMB: K_(m) = 4.11 mM, 4 Solution reaction Wang, Gao V_(max) = 55.56 × 10⁻⁸ M s⁻¹; at room et al. 2018 H₂O₂: K_(m) = 6.41 mM, temperature V_(max) = 10.2 × 10⁻⁸ M s⁻¹ Fe₂O₃ NP: K_(m) = 36.82 mg/L, 8 Solution reaction Pariona V_(max) = 1.36 mg/min, at room et al. 2016 k_(cat) = 0.273 min⁻¹ temperature 2LFh NP: K_(m) = 46.67 mg/L, 8 Solution reaction Pariona V_(max) = 1.17 mg/min, at room et al. 2016 k_(cat) = 0.234 min⁻¹ temperature PdCu TMB: K_(m) = 0.25 mM, 4 Microwave- He et al. V_(max) = 1.19 × 10⁻⁸ M s⁻¹, assisted 2018 k_(cat) = 20.2 × 10⁻⁵ s⁻¹; wet-chemical H₂O₂: K_(m) = 3.05 mM, synthetic approach V_(max) = 6.25 × 10⁻⁶ M s⁻¹, k_(cat) = 10.61 × 10⁻² s⁻¹; Co₉S₈ TMB: K_(m) = 1.64 mM, 3 Heating and Mu et al. V_(max) = 99 × 10⁻⁸ M s⁻¹; precipitation 2018 H₂O₂: K_(m) = 7.39 mM, V_(max) = 35 × 10⁻⁸ M s⁻¹ Cu(OH)₂ SC TMB: K_(m) = 2.448 mM, 4.5 Solution reaction Cai et V_(max) = 44.83 × 10⁻⁸ M s⁻¹; at room al. 2015 H₂O₂: K_(m) = 0.199 mM, temperature V_(max) = 42.51 × 10⁻⁸ M s⁻¹ Ru frame TMB: K_(m) = 0.0603 mM,  0-12 Heating and Ye et al. V_(max) = 13.4 × 10⁻⁸ M s⁻¹; precipitation 2016 H₂O₂: K_(m) = 318 mM, V_(max) = 7.41 × 10⁻⁸ M s⁻¹ FePt-Au HNP TMB: K_(m) = 0.445 mM, 4 Hydrothermal Ding et V_(max) = 24.67 × 10⁻⁸ M s⁻¹; method al. 2018 H₂O₂: K_(m) = 0.0185 mM, V_(max) = 0.6894 × 10⁻⁸ M s⁻¹ PtAg-MoS₂ TMB: K_(m) = 25.71 mM, 4 Heating and Cai et V_(max) = 7.29 × 10⁻⁸ M s⁻¹; precipitation al. 2016 H₂O₂: K_(m) = 0.386 mM, V_(max) = 3.22 × 10⁻⁸ M s⁻¹ PtPd NP TMB: K_(m) = 1.78 mM, 9.5 Reduction and Jiang et V_(max) = 36.4 × 10⁻⁸ M s⁻¹; mild heating al. 2016 H₂O₂: K_(m) = 0.053 mM, V_(max) = 9.26 × 10⁻⁸ M s⁻¹ Cu-hemin TMB: K_(m) = 1.42 mM, 6 Reduction and Liu et V_(max) = 26.22 × 10⁻⁸ M s⁻¹; mild heating al. 2016 H₂O₂: K_(m) = 2.18 mM, V_(max) = 116 × 10⁻⁸ M s⁻¹ PS@Au@PB TMB: K_(m) = 1.22 mM, 5.2 Solution reaction Zhang et V_(max) = 59 × 10⁻⁸ M s⁻¹; at room al. 2016 H₂O₂: K_(m) = 0.17 mM, temperature V_(max) = 38.9 × 10⁻⁸ M s⁻¹ Cu NC TMB: K_(m) = 0.648 mM, 6 Solution reaction Hu et al. V_(max) = 5.96 × 10⁻⁸ M s⁻¹; and mild heating 2016 H₂O₂: K_(m) = 29.16 mM, V_(max) = 4.22 × 10⁻⁸ M s⁻¹

Exemplary Embodiments of the Invention

The present invention provides a process for treating contaminated water with hydrogen peroxide in the presence of a Fenton-like catalyst (e.g., an iron oxychloride catalyst). The process degrades the contaminants in the water to benign constituents. The process enables water treatment in the absence of acid.

Embodiments of the invention are described below:

In certain embodiments, a process for treating contaminated water, comprising contacting said contaminated water with hydrogen peroxide in the presence of a Fenton-like catalyst, wherein the process occurs in the absence of an acid.

In certain embodiments, a process for treating contaminated water, comprising contacting said contaminated water with hydrogen peroxide in the presence of an iron oxychloride catalyst, wherein the process occurs in the absence of an acid.

In certain embodiments, the contaminated water is subjected to an electric current. In certain embodiments, the contaminated water is subjected to an electric current of about 100 mA.

In certain embodiments, the contaminated water subjected to the electric current attains a pH of about 2 to about 4. In certain embodiments, the contaminated water subjected to the electric current attains a pH of about 2.9 to about 3.2. In certain embodiments, the contaminated water subjected to the electric current attains a pH of about 3.

In certain embodiments, the iron oxychloride catalyst is a FeOCl/Al₂O₃ composite. In certain embodiments, the iron oxychloride catalyst is immobilized on a support. In certain embodiments, the iron oxychloride catalyst is immobilized on a γ-Al₂O₃ support. In certain embodiments, FeOCl nanoparticles are immobilized on a porous γ-Al₂O₃

In certain embodiments, the hydrogen peroxide is converted to hydroxy radicals. In certain embodiments, the hydroxy radical is the species that reacts with the contaminant(s), causing degradation of the contaminant(s).

In certain embodiments, a process for treating contaminated water, comprising:

(i) adding hydrogen peroxide to the contaminated water;

(ii) providing an influent stream of the contaminated water into a chamber comprising an upstream anode, a downstream cathode, and Fenton-like catalyst between the anode and cathode;

(iii) applying an electric current to the chamber to provide an acidic environment in the chamber so as to thereby treat the contaminated water in the chamber; and

(iv) collecting an effluent stream of the treated water exiting the chamber.

In certain embodiments, the treatment occurs in the absence of acid, i.e., acid is not added at any step of the process.

In certain embodiments, a process for treating contaminated water, comprising:

(i) adding hydrogen peroxide to the contaminated water;

(ii) providing an influent stream of the contaminated water into a chamber comprising an upstream anode, a downstream cathode, and an iron oxychloride catalyst between the anode and cathode;

(iii) applying an electric current to the chamber to provide an acidic environment in the chamber so as to thereby treat the contaminated water in the chamber; and

(iv) collecting an effluent stream of the treated water exiting the chamber.

In certain embodiments, the treatment occurs in the absence of acid, i.e. acid is not added at any step of the process.

In certain embodiments, the influent stream of contaminated water is at neutral pH. In certain embodiments, the influent stream of contaminated water has a pH of about 7 to about 8.

In certain embodiments, the effluent stream of treated water is at neutral pH. In certain embodiments, the influent stream of contaminated water has a pH of about 7 to about 8.

In certain embodiments, the contaminated water in the chamber is at an acidic pH. In certain embodiments, the pH of the contaminated water in the chamber is about 2 to about 4. In certain embodiments, the pH of the contaminated water in the chamber is about 2.9 to about 3.2. In certain embodiments, the pH of the contaminated water in the chamber is about 3.

In certain embodiments, anode and cathode are mixed metal oxide electrodes. In certain embodiments, the electric current is about 100 mA. In certain embodiments, the electric current enables an acidic pH between the anode and cathode to be attained at steady state.

In certain embodiments, the iron oxychloride catalyst is a FeOCl/Al₂O₃ composite. In certain embodiments, the iron oxychloride catalyst is immobilized on a support. In certain embodiments, the iron oxychloride catalyst is immobilized on a γ-Al₂O₃ support. In certain embodiments, FeOCl nanoparticles are immobilized on a porous γ-Al₂O₃

In certain embodiments, the hydrogen peroxide is converted to hydroxy radicals inside the chamber. In certain embodiments, the hydroxy radical is the species that reacts with the contaminant(s), causing degradation of the contaminant(s). In certain embodiments, the concentration of hydroxy radicals in the chamber is greater than 250 μM.

In certain embodiments, the flow rate of the water through the chamber is less than 30 mL/min. In certain embodiments, the flow rate of the water through the chamber is about 10 to about 25 mL/min. In certain embodiments, the flow rate of the water through the chamber is about 10 to about 20 mL/min. In certain embodiments, the flow rate of the water through the chamber is about 15 mL/min.

In certain embodiments, the flow rate of the water through the chamber is 30-50 mL/min. In certain embodiments, the flow rate of the water through the chamber is 50-100 mL/min. In certain embodiments, the flow rate of the water through the chamber is 100-500 mL/min. In certain embodiments, the flow rate of the water through the chamber is 500-1000 mL/min.

In certain embodiments, the treating comprises purification of the water by removal of contaminants from the water. In certain embodiments, the treating comprises removing one or more contaminants from the water. In certain embodiments, the treating comprises removing one or more organic contaminants from the water. In certain embodiments, the treating comprises removing one or more drugs, drug precursors, plastic precursors, herbicides, pesticides, or recalcitrant dyes from the water.

In certain embodiments, the treating comprises removing bisphenol A (BPA) from the water. In certain embodiments, the treating comprises removing greater than 99% of the bisphenol A (BPA) present in the water prior to treatment of the water. In certain embodiments, the treating comprises removing greater than 95% of the bisphenol A (BPA) present in the water prior to treatment of the water. In certain embodiments, the treating comprises removing greater than 90% of the bisphenol A (BPA) present in the water prior to treatment of the water. In certain embodiments, the treating comprises removing greater than 80% of the bisphenol A (BPA) present in the water prior to treatment of the water.

In certain embodiments, the contaminant(s) is degraded to carbon dioxide and water. In certain embodiments, the bisphenol A (BPA) is degraded to carbon dioxide and water.

Chemicals

FeCl₃.6H₂O (Honeywell Fluka) was used to synthesize the FeOCl nanocatalyst, and H₂O₂ was purchased from Fisher Scientific. γ-Al₂O₃(Alfa Aesar) was used as a support to immobilize FeOCl. BPA (Sigma-Aldrich), ibuprofen (Alfa Aesar), atrazine (Sigma-Aldrich), carbamazepine (Sigma-Aldrich), 4-chlorophenol (Acros Organics), 4-nitrophenol (Acros Organics), Rhodamine B (Harleco, Philadelphia, Pa.), Reactive blue 19 (Sigma-Aldrich), and Orange II (Acros Organics) were used as substrates for Fenton-like process treatment. Other chemicals (i.e., sodium sulfate (Na₂SO₄) as the supporting electrolyte, sodium carbonate (Na₂CO₃) for synthetic alkaline water, ethanol as a HO. radical scavenger, methanol and acetonitrile as mobile phase for HPLC) were purchased from Fisher Scientific. Pure water was used throughout the work except the field water studies.

Synthesis of FeOCl

2 g grinded FeCl₃.6H₂O powder was put at the bottom of a ceramic crucible, and then tightly sealed with aluminum foil. The crucible was heated at an 8° C./min rate until up to 200° C. and maintained for 2 h in a muffle furnace. After heating, the crucible was naturally cooled down to room temperature. The cooling process took around 1 h. The formed dark red FeOCl plates were ground into fine powder and then washed with ethanol at least for three times until eluent was colorless to remove residual FeCl₃ impurity. Eventually, the synthesized and purified FeOCl was stored in a dry 15-mL Corning tube, and then put in a chemical fume hood under constant ventilation drying.

Synthesis of FeOCl/Al₂O₃

10 g grinded γ-Al₂O₃ microparticles were mixed with 5.97 g FeCl₃.6H₂O (i.e., theoretical 10 wt % Fe loading) under vigorous vortex for 10 min until the powder mixture turned homogeneously yellow. The powder was then transferred into 5-mL glass tubes with air-tight caps and further sealed with Teflon bands to prevent vaporization of crystalline water in FeCl₃.6H₂O. The glass tubes were heated under 80° C. for 12 h, during which FeCl₃.6H₂O (melting point 37° C.) infiltrated into γ-Al₂O₃ pores. The obtained powder was transferred into crucibles for the synthesis of FeOCl/Al₂O₃ using the same condition as FeOCl synthesis. Produced FeOCl/Al₂O₃ was extensively washed with ethanol before use.

Synthesis of FeOCl on Alginate Hydrogel

1.5 g synthesized FeOCl and 3 g alginate were at first sufficiently mixed via vigorous vortex, and then 100 mL DI water was poured into the beaker containing well-mixed FeOCl and alginate. A clean glass stick was used to stir the solution until it turned into homogeneous red paste. A syringe was then used to drop the red slurry into 0.1 M CaCl₂) solution, and formed FeOCl/alginate beads were allowed to harden for 2 h. The as-prepared FeOCl/alginate beads were then washed with DI water and loaded into the reactor for subsequent experiments.

Characterization of Materials

The crystalline phase of samples was measured using a D/MAX-2200 X-ray diffraction (XRD) analyzer equipped with a rotation anode using CuKa radiation (λ=0.1541 nm). Field emission scanning electron microscope (FESEM) photography was performed on an S-4800 instrument at an accelerating voltage of 15 kV. High resolution transmission electron microscopy (HRTEM) images were obtained on a JEOL JEM-2100F transmission electron microscope at an accelerating voltage of 200 kV. The chemical composition and the binding states on the surface of the FeOCl specimen were carried out on a Thermo Scientific ESCALAB 250 Xi X-ray photoelectron spectroscopy (XPS) microprobe with monochromatic X-ray (Al Kα, 1486.6 eV) radiation as an excitation source. The measurements of specific surface area, pore volume, and pore size distribution in the 2-500 nm range were carried out using a Micromeritics ASAP 2020 instrument by nitrogen adsorption/desorption at 77.3 K (−194.85° C.).

EFL Platform Loading Unimmobilized FeOCl

5 g FeOCl powder was mixed well with 50 g sand particles under vortex for 20 min, and the mixture was then filled in between the cathode and anode, and all other spaces were filled with sand particles to reduce hydrodynamic perturbation. A neutral solution containing 10 mM H₂O₂, 10 μM BPA, and 5 mM Na₂SO₄ as electrolyte was pumped up into the vertically aligned reactor at a rate of 15 mL/min. A steady-state acidic-compartment was formed between the cathode and anode under a current of 100 mA after 60 min, and BPA removals at each sampling port was tested.

Flow-Through Column Reaction

The experimental column (15 cm×5 cm O.D., 0.32 cm wall thickness) is made with cast acrylic tube and Teflon rods with O-rings as the top and bottom cap. Mixed metal oxide sintered titanium (Ti/MMO) mesh electrodes were inserted in parallel at a distance of 9 cm. Titanium hex nuts and threaded rods were used to connect Ti/MMO electrodes with electric power source. Gum rubber was sealed on the external titanium rod to avoid contact with both electrodes. Four sampling ports using tube adapter (0.79375 cm tube to 0.3175 cm NPT male) were installed at an equal distance (3 cm) between the electrodes.

To load catalysts into the reactor, the FeOCl/Al₂O₃ catalyst (˜50 g) was filled between the cathode and anode, and rest spaces were filled with fine silica sand particles. The silica sand particles were extensively washed with pure water, and then oven-dried at 80° C. Filter papers were placed at the bottom and top of sand zones to avoid particles draining into effluent.

Initially, a neutral solution (pH 7) of 10 μM BPA was used to condition the column until effluent BPA concentration matched influent to reach adsorption equilibrium. After BPA breakthrough, another neutral solution containing 10 mM H₂O₂, 10 μM BPA, and 5 mM Na₂SO₄ electrolyte was pumped up into the vertically aligned column at a rate of 15 mL/min by a peristaltic pump, with a 100 mA electric current applied to the electrodes. A steady-state acid-compartment was formed between electrodes after 60 min, and BPA removal was tested. 1 mL solutions sampled from each port and influent/effluent were neutralized with 1 mL 20 mM phosphate buffer (pH 7) to avoid following analysis inaccuracy due to pH inconsistence. Samples after filtration with 0.45 μm PVDF membrane (13 mm diameter, Jin Teng Ltd., China) were measured by high-performance liquid chromatography (HPLC, Agilent 1200 Infinity Series) equipped with an Agilent Eclipse AAA C18 column (4.6×150 mm). BPA was separated by 0.5 mL/min methanol/water 60/40 mobile phase, and detected at 228 nm wavelength using Agilent 1260 diode array detector. Degradation of other substrates was also tested, and quantification methods were indicated in

TABLE 2 Detection Flow Rate Detection Substrate Method Mobile Phase Ratio (mL/min) Wavelength Ibuprofen HPLC methanol/water 68/32 0.5 228 nm Atrazine HPLC methanol/water 60/40 0.5 228 nm Carbamazepine HPLC methanol/water 60/40 0.5 285 nm 4-Chlorophenol HPLC acetonitrile/water 30/70 0.5 225 nm 4-Nitrophenol HPLC acetonitrile/water 60/40 0.5 280 nm Rhodamine B UV-Vis — — — 554 nm Spectrometer Reactive UV-Vis — — — 592 nm Blue 19 Spectrometer Orange II UV-Vis — — — 485 nm Spectrometer

In certain assays, the solution pH, flow rate, and synthetic alkalinity (i.e., 1 mM Na₂CO₃ is equivalent to 100 mg CaCO₃/L water alkalinity) were subjected to changes as indicated, while other parameters were fixed as stated above. For electricity responsiveness test, experiment was initiated by turning on the 100 mA electric current after conditioning the column, without reaching steady state. For BPA removal in field water bodies, water samples 1 and 2 were taken from lakes in Boston, Mass., US, and water samples 3 and 4 were taken from underground sources of Superfund sites in Puerto Rico. They were stored at 4° C. cold room. Characterizations of the field water samples were shown in Table 3. Water samples were filtrated through 0.45 μm PVDF membranes (47 mm diameter, EMD Millipore, Germany) before use to remove suspended particles. Solution pH was not adjusted after addition of H₂O₂ and BPA, and solution intrinsic conductivity supported electrochemical water splitting. BPA concentrations in the influent and effluent were analyzed during steady state.

TABLE 3 Total organic Dissolved Water Sample Water type carbon (mg/L) oxygen Sample 1 Lake water 21.4 8.38 Sample 2 Lake water 115.5 7.49 Sample 3 Underground 87.2 7.92 water Sample 4 Underground 158.7 7.21 water Hydroxyl Radical Quantification Method

The total HO. radical amount was quantified via a reported benzoic acid oxidation method⁴⁸. Briefly, the accumulated HO. radical amount equals that of generated p-hydroxybenzoic acid, a product of HO. radical and benzoic acid reaction, multiplied by a conversion factor of 5.87. In batch reaction, 100 mL solutions of 5 mM benzoic acid, 10 mM H₂O₂, and 0.2 g/L catalyst (i.e., free FeOCl or immobilized FeOCl/Al₂O₃) were stirred for 30 min under indicated solution pH. In flow-through reaction, after conditioning the column with 5 mM benzoic acid until breakthrough, influent solutions containing 5 mM benzoic acid, 10 mM H₂O₂, and 5 mM Na₂SO₄ at neutral pH passed through the column at a rate of 15 mL/min, with or without 100 mA electric current applied to the electrodes. Effluent samples were collected during steady state. The concentration of generated p-hydroxybenzoic acid was analyzed by HPLC with mobile phase of 0.5 mL/min methanol/water 20/80 and detection wavelength at 255 nm using the same column for BPA analysis.

Density Functional Theory (DFT) Calculation Method

Geometry optimization. DFT calculations were performed with PBE (Perdew-Burke-Ernzerhof) functional by using CASTEP (Clark et al. 2005; Segall et al. 2002) as incorporated in Materials studio 7.0. The ultrasoft pseudopotential (USPP) was used to represent the core-valence electron interaction. The plane wave expansion basis sets with a cut-off energy of 300 eV was used. The k-point sampling of 4×4×2 within the Monkhorst-Pack special k-point scheme in the Brillouin Zone was considered for the geometry optimization and energy calculation.

Transition state calculation. To investigate the pathways of Fenton process, linear synchronous transit/quadratic synchronous transit (LST/QST) by using DFT+U technique were performed, and the Uvalues of O 2p and Fe 3d is 6.3 and 3.0 eV, respectively. FeOCl (100) surface was considered as reactive surface with two fixed atomic layers (Lahay et al. 2007), and 2×2×1 k-point mesh was used. Spin polarization was considered for all the calculations.

Reactive Transport Model to Estimate the Steady-State pH in the Ella Process

Water splitting is considered as the dominant electrolysis reaction in this system. This process will produce an acid front after the anode and gets neutralized after passing through the cathode. Anode: 2H₂O→O₂+4H⁺+2e ⁻  (1) Cathode: 2H₂O+2e ⁻→H₂+2OH⁻  (2)

Competing reactions may exist depending on the electrolyte composition and concentration, which reduces the current efficiency of the system. However, in this study we assume 100% efficiency for water electrolysis on both electrode surfaces.

Transport process in the column is expressed by Nernst-Plank's equation in dilute electrolytes. J _(i) =uC _(i)-D _(H) _(i) ∇C _(i)-u _(i) z _(i) FC _(i)∇ϕ  (3) Where u is the pore water velocity and J_(i), C_(i), D_(H) _(i) , u_(i), and z_(i) are the total flux, concentration, hydrodynamic dispersion coefficient, mobility, and the charge of i^(th) species, respectively. Species mobility, u_(i), can be estimated by Einstein relation.

$\begin{matrix} {u_{i} = \frac{z_{i}{FD}_{i}}{RT}} & (4) \end{matrix}$

Hydrodynamic dispersion, D_(H), is a function of the pore water velocity and is represented as D_(H)=τD₀+α_(L)u, where the tortuosity, τ, is a measure of effective transport path through media, D₀, is the molecular diffusion coefficient, and α_(L), is the longitudinal dispersivity. Many studies are conducted to evaluate the hydrodynamic dispersion coefficient (De Smedt et al. 1984). This factor in large scale systems is estimated by column tracer test or fitted models of similar experiment characteristics.

In systems with supporting electrolyte, migration term can be neglected. Therefore, the governing equation for a transient simulation is obtained by conservation of mass.

$\begin{matrix} {\frac{\partial C_{i}}{\partial t} = {{- {\nabla J_{i}}} + R_{i}}} & (5) \end{matrix}$

Where R_(i) is the reaction rate of species i in the bulk fluid. Electric field in the electrolyte can be calculated considering conservation of charge in the electrolyte, knowing that current arises from the motion of all charged species. i=−κ∇ϕ−κFΣ _(i) z _(i) D _(i) ∇C _(i)  (6)

Where the first term is ohmic potential and the second term is concentration-caused potential. In systems with supporting electrolyte, the concentration gradient can be neglected and the equation reduces to i=−κ∇ϕ  (7) where κ=F ²Σ_(i) z _(i) ² u _(i) C _(i)  (8)

The inlet boundary condition is considered Dirichlet boundary with a constant feed concentration over time. C(x=0,t)=C ₀  (9)

The outlet boundary condition is a Neumann boundary condition: ∇C _(i)=0  (10)

Fluxes on the surface of the electrodes are shown as followed. J _(i)|_(x=electrode+∂x) =J _(i)|_(x=electrode−∂x) +J _(eRXN,i)  (11) where, J_(eRXN,i), is the inward electrochemical source/sink flux for i^(th) species and is calculated in a constant current operating condition using Faraday's law.

$\begin{matrix} {J_{{eRXN},i} = \frac{I}{z_{i}{FA}}} & (12) \end{matrix}$ I applied current z_(i) number of electrons participating for each mole of species i produced/consumed F Faraday's constant, 96485 c/eq A Electrode surface area

The homogeneous phase reactions included in the model are assumed to reach equilibrium. Σ_(j=1) ^(N) ^(c) ν_(ij) C _(i)=0 for i=1, . . . ,N _(x)  (13) N_(c) total number of species N_(x) total number of reactions ν_(ij) stochiometric constant for j^(th) species in the i^(th) reaction

There have been many studies on integration of species transport and equilibrium reaction models (Acar et al. 1993; Davis et al. 2003; Hojabri et al. 2018; Paz-Garcia et al. 2016; Steefel et al. 1994). In this study, reaction simulations and species concentrations are determined by PHREEQC computer program (Parkhurst et al. 2013). PHREEQC is a computer program which is designed and optimized for aqueous geochemical reactions with a strong database. Nardi et al. have developed a comprehensive geochemical model using COMSOL Multiphysics for transport calculations and PHREEQC for geochemical reaction calculations (Nardi et al. 2014). Paz Garcia et al. have obtained a similar approach in simulation of electrochemical remediation reactors using COMSOL Multiphysics with an interface with PHREEQC. In our study, we used MATLAB as the main platform for numerical calculation with an interface with PHREEQC for chemical reaction calculations. The interface written in MATLAB is used to transfer data between MATLAB and PHREEQC using Microsoft COM (Component Object Model). Phreeqc.dat is the thermodynamic database used in this study for equilibrium calculations. The reactions in the bulk fluid include acid/base reactions, water association/dissociation reaction, and redox reactions. Due to the characteristics of the aqueous reactions in this system, local equilibrium is considered.

In this study, hybrid Finite Volume differencing scheme is used for spatial discretization and implicit scheme is used for temporal discretization with a non-iterative sequential solver for integration of reactions in the simulation. This scheme guarantees continuity of the concerned variables and stability of numerical simulation. The hybrid scheme will evaluate the differencing scheme based on local Peclet number.

$\begin{matrix} {{Pe} = \frac{u}{D/L}} & (14) \end{matrix}$

If the local Peclet number is small, diffusion is dominant and central differencing scheme results in smaller error. However, if the advection is dominant, upwind scheme is used to more accurately capture the impact of advection (Versteeg et al. 2007).

Example 1. Design of a Flow-Through Water Treatment Platform

Ella process was utilized to regulate pH of heterogeneous Fenton-like catalysts for water treatment with desired acidity. To this end, immobilized catalysts must be transferred to the acidic zone mediated by the Ella process, whereby H₂O₂ is rapidly transformed into oxidizing HO. radicals, leading to the instant degradation of organic compounds in the local vicinity (FIG. 1A). This coupled water treatment process is categorized as electro-Fenton-like (EFL) platform in this study. The flow-through treatment method is especially favored over batch reaction mode for industry application, since a water treatment plant treats high volume of contaminated water in a fast pace. Besides, it is worth of noting that the EFL platform can take advantage of the intermittent solar and wind electricity, often with near-zero or even negative prices.

The contaminants treatment efficiency by the EFL platform is majorly determined by the reaction during the transport through catalyst column, that is, longer retention time and higher catalyst and H₂O₂ concentration tend to result in more complete contaminants removal. Therefore, the key aspects to warrant the success of the EFL platform are to promote HO. generation and allow sufficient reaction time within the column.

pH Regulation by the Ella Process

As a proof of concept, a benchtop flow-through device was manufactured for our EFL platform. A set of stable mixed metal oxide electrodes were installed 9 cm apart in a vertically anchored acrylic flow-through column device (15 cm×5 cm O.D.). The column was filled with clean silica sand (0.15 to 0.6 mm) to maintain a laminar flow. A combination of 100 mA electric current and 15 mL/min hydraulic flow rate was applied to the neutral solution passing through the column, and solution pHs at various locations along the column were measured (FIG. 1B). The solution was homogeneously neutral without electric current; however, by turning on the 100 mA electric current, an acidic pH of 2.93-3.12 between the anode and cathode was automatically attained at steady state. The electrochemically created acidity is suitable for most Fenton-like catalysts. The effluent pH measured as 7.59 was close to the influent value (pH 7), showing minimal effect on the treated water pH. A reactive transport model that accounts for advection, hydrodynamic dispersion, and ion migration was used to simulate the pH profile (Hojabri et al. 2018). Modeling results indicate that the theoretical acidity of the confined space between electrodes using the above stated experimental settings is pH 2.8. The slight discrepancy of pH between experimental results and modelled value is possibly because the current efficiency of water electrolysis was not 100% due to possible energy losses in a non-ideal system.

Immobilization of Fenton-Like Catalyst

Iron oxychloride (FeOCl) was reported to possess extraordinary Fenton-like activity with high fidelity and can be mass produced (Sun et al. 2018; Yang et al. 2013). Characterizations of the synthetic FeOCl nanocatalyst produced via the calcination of FeCl₃.6H₂O were shown in FIGS. 2 and 3 . Bisphenol A (BPA) was used as the primary pollutant to illustrate FeOCl catalytic degradation performance, provided BPA is an environmental estrogen that disrupts human endocrine system upon exposure (Vanderberg et al. 2007). 10 μM BPA was rapidly degraded by the FeOCl/H₂O₂ reaction. On the contrary, the addition of ethanol, a strong HO. radical quencher (Adams et al. 1965), competed with BPA for the produced HO. radical reservoir and fully inhibited BPA removal by FeOCl/H₂O₂ reaction, demonstrating the degradation of BPA was via HO. radical (FIG. 10 ). The activity of synthesized FeOCl sample was tested by decomposing H₂O₂ for BPA removal. It was shown that 0.2 g/L FeOCl with 10 mM H₂O₂ at pH 3 could remove 86% 10 μM BPA in 6 min and 100% BPA in 8 min. The role of HO. radical in BPA removal was verified by ethanol as a scavenger, since it fully inhibited BPA removal via quenching HO. radical. The catalytic activities of FeOCl at different pHs were compared. Results showed that, the optimum pH for FeOCl is around pH 3 as it mediated the highest yield of HO. radical. It was further found that FeOCl showed optimal activity at pH 3, around 9.3-fold higher than that at pH 7 in terms of HO. radical yield (FIG. 4B).

Density functional theory (DFT) calculation was harnessed to study the catalysis mechanism of the FeOCl/H₂O₂ reaction. It was revealed that the reaction is accomplished via two electron-transfer processes (FIG. 5 ). In the first step, Fe^(III)OCl is at first reduced by H₂O₂ into Fe^(II)OCl, and the second step the derived Fe^(II)OCl then decomposes H₂O₂ into HO. radical via homolytic cleavage. The readily reducible nature of unsaturated Fe atoms on the exposed (100) surface of FeOCl crystals allows rapid turnovers of Fe^(III/II) to catalyze the H₂O₂ transformation. Specifically, the energy barrier of reducing Fe^(III) to Fe^(II) on FeOCl crystals by H₂O₂ was determined to be 0.235 eV (FIG. 6 ), whereas that of hematite (Fe₂O₃, a rhombohedral Fenton-like catalyst) is 0.76 eV as a comparison (Ji et al. 2019).

It is, however, a great concern that the micro catalyst particles are subject to fluid transport, resulting in potential draining from the silica sand pores within the column device. For instance, by packing well-mixed FeOCl and silica sand particles into the column (FIG. 7 ), the overall catalyst activity decayed by 36% after 8 h due to hydraulic erosion (FIG. 8 ). Another immobilization strategy of cross-linking FeOCl with alginate hydrogel was attempted for effective retention of FeOCl nanoparticles (FIG. 9 ) (Smidsrød et al. 2019). However, the resulting FeOCl/alginate composite showed only 1% activity compared to the same amount of unimmobilized FeOCl catalyst (FIG. 10 ), delivering poor in-reactor performance under high flow rates (FIGS. 11 and 12 ). At pH 3, 0.2 g/L FeOCl and 10 mM H₂O₂ mediated formation of 305.3 μM HO. radical (FIG. 4B) after 30 min, while 0.075 g/mL FeOCl/alginate (dry weight, 1:2 FeOCl:alginate) produced 396.2 μM HO. radical (FIG. 10B). As a result, the specific activity of unimmobilized and immobilized FeOCl was calculated as 1511.5 and 15.8 μM HO./(g L⁻¹) FeOCl, respectively. This is due to a large fraction of FeOCl particles becoming buried inside the hydrogel of the FeOCl/alginate composite and were not effectively accessible by H₂O₂ molecules.

To solve this problem, FeOCl nanoparticles were alternatively immobilized on a porous γ-Al₂O₃ support via a melt infiltration method (FIG. 13A) (Eggenhuisen et al. 2010), with the belief that this approach offers maximum FeOCl catalytic sites for H₂O₂ molecules. Field emission scanning electron microscopy (FESEM) images clearly revealed the dispersion of FeOCl nanosheets on the amorphous γ-Al₂O₃ support in the synthesized FeOCl/Al₂O₃ composite (FIGS. 13B-13D), with a surface area of 206 m²/g (Table 4). The compositional distribution of the FeOCl/Al₂O₃ was investigated with energy-dispersive X-ray spectroscopy (EDX) (FIG. 13E). EDX analysis identified Al, O, Fe, and Cl elements on the FeOCl/Al₂O₃ composite. Elemental mapping results suggested that Al and Fe elements were separately located, in agreement with the overlay structure of the FeOCl/Al₂O₃ composite. Besides, Cl element exhibited consistent pattern with Fe element on the FeOCl surface, while O element was uniformly distributed on the FeOCl/Al₂O₃ composite. X-ray diffraction (XRD) of the FeOCl/Al₂O₃ composite disclosed several characteristic diffraction peaks (2θ) at 11.2, 26.1, and 35.4°, which respectively belongs to the (010), (110), and (O₂₁) plane of orthorhombic FeOCl crystal (PDF 01-072-0619) (FIG. 13F). The chemical states of compositional elements were studied with X-ray photoelectron spectroscopy (XPS). In particular, deconvoluted Fe 2p spectrum showed Fe³⁺2p_(1/2) (724.6 eV) and 2p_(3/2) (711.2 eV) were dominant over Fe²⁺2p_(1/2) (728.2 eV) and 2p_(3/2) (714.6 eV) (FIG. 13G), consistent with the unimmobilized FeOCl crystal (FIG. 3 ). XPS analyses of other elements in the FeOCl/Al₂O₃ composite and the γ-Al₂O₃ support are shown in FIGS. 15 and 18 . Overall, the above results suggested that the morphology and electronic properties of the FeOCl crystal remained intact after immobilization on the γ-Al₂O₃ support.

TABLE 4 γ-Al₂O₃ FeOCl/Al₂O₃ BET Surface Area 883.9819 m²/g 212.7531 m²/g Pore BJH Adsorption 1.396243 cm³/g 0.577339 cm³/g Volume cumulative volume of pores between 1.7 nm and 300 nm width BJH Desorption 1.401154 cm³/g 0.556347 cm³/g cumulative volume of pores between 1.7 nm and 300 nm width Pore Adsorption average 5.92993 nm 10.94665 nm Size pore diameter (4V/A by BET) BJH Adsorption 7.8207 nm 8.7791 nm average pore width (4V/A) BJH Desorption 7.0510 nm 9.1477 nm average pore width (4V/A)

Activity test results of the synthetic FeOCl/Al₂O₃ composite are shown in FIG. 16 . It was found that 10 μM BPA was completely degraded in 10 min by 0.2 g/L of FeOCl/Al₂O₃ and 10 mM H₂O₂ at pH 3, while the FeOCl/Al₂O₃ composite or H₂O₂ alone led to negligible BPA removals. Further, under the stated conditions, FeOCl/Al₂O₃-mediated Fenton-like reaction produced the most remarkable amount of HO. radicals at pH 3 (i.e., 289.8 μM after reaction for 30 min), which acidity could be readily achieved by the Ella process. The catalytic performance of the FeOCl/Al₂O₃ composite showed a consistent pattern with that of the unimmobilized FeOCl nanoparticle (FIG. 4 ), indicating that the γ-Al₂O₃ support played no role in H₂O₂ transformation.

Example 2. High Performance of the Electro-Fenton-Like Platform

The synthetic FeOCl/Al₂O₃ composites were transferred to the space between electrodes of the column, in order to utilize the acidity produced by the Ella process (FIG. 17A). Neutral solutions containing 10 mM H₂O₂ oxidant and 10 μM BPA contaminant were pumped through the column at a rate of 15 mL/min, and BPA removals along the hydraulic flux direction were measured (FIG. 17B). Low BPA removal from the effluent (17.6%) was observed without electric current, due to the weak activity of FeOCl/Al₂O₃ under neutral condition. However, after a 100 mA electric current was applied to electrodes, gradual degradation of BPA took place as measured from the sampling ports, and BPA removal reached 100% in the effluent. Direct BPA degradation by electrodes was ruled out based on control experiment (FIG. 18 ). Additionally, the presence of 10 mM ethanol as HO. radical scavenger almost fully quenched BPA removal (FIG. 18 ), suggesting that in situ produced HO. radicals accounted for BPA degradation. As shown in FIG. 19 , the HO. radicals generated by the EFL platform could also non-selectively degrade other organic contaminants including drugs (ibuprofen and carbamazepine), herbicide (atrazine), pesticide and drug precursors (4-chlorophenol and 4-nitrophenol), and recalcitrant dyes (rhodamine B, reactive blue 19, and orange II). It was further determined that the yield of HO. radical produced by the platform when 100 mA electric current was turned off and on was 23.5 and 254.4 μM, respectively (FIG. 17C). This 10.8-fold increase in HO. radical production was attributed to the acidic environment created by the Ella process which boosted FeOCl/Al₂O₃ catalyst activity. Results indicate that the EFL platform by coupling a heterogeneous Fenton-like catalyst and the Ella process in a flow-through column device is effective for removal of organic contaminants.

The long-term stability of BPA removal by the EFL platform was tested (FIG. 17D). Over the course of 8-h reactions, laminar fluid transport was maintained, and the BPA removal steadily approached 100%. BPA removal by this platform under different hydraulic flow rates was also measured (FIG. 17E). A high flow rate leads to shortened contact time among H₂O₂ molecules, the catalyst surface, and the organic contaminant, which reduces HO. radical yield and compromises contaminant removal. Over 95% of 10 μM BPA could be removed from the effluent at a flow rate of less than 20 mL/min, whereas BPA removal rate decreased to 82.4% and 44.4% at 25 and 30 mL/min, respectively. The tolerance of flow rate by using FeOCl/Al₂O₃ in this design was greatly superior than that by using FeOCl crosslinked on alginate hydrogel as a catalyst (FIG. 12 ), primarily due to the abundant catalytic sites exposed on the surface of the FeOCl/Al₂O₃ composite.

Responsiveness of BPA removal by the EFL platform to electric current was monitored by repeatedly turning the electric power supply on and off with a 60-min interval. As shown in FIG. 17F, BPA removal significantly increased after the 100 mA electric current was turned on for 15 min, and approached 100% after 40 min. As the power was turned off, BPA removal gradually decreased during the first 30 min, from 84.3-92.3% to 16.7-23.9%, and was steady afterwards. The non-instant response of BPA removal to electricity was presumably because of the slow accumulation and desorption of protons. Results demonstrated that electricity is a critical governor of contaminant removal by our developed platform. In addition, the observed response time in this study matches well with the intermittency of solar and wind electricity, and therefore our device can potentially provide clean drinking water without the need for battery energy storage.

Complex water environments are typically encountered in water treatment practices, posing challenges to downgradient treatment. For instance, water bodies receiving leachates from industries could be highly basic and require a pH neutralization process such as CO₂ sequestration before biological/chemical treatment (Gomes et al. 2016). In this study, contaminants in a synthetic basic solution are treated by the EFL platform. Influent solutions of pH 7-11 were effectively acidified to around pH 3 under 100 mA electric current and 15 mL/min flow rate, in good agreement with modeling results (FIG. 20A). Consequently, BPA removals approached 100% under the Ella process-mediated acidic environment regardless of influent pH, whereas less than 22.4% of BPA was removed when the electric current was turned off (FIG. 20B).

The potential of water bodies to neutralize protons, namely water alkalinity, represents another challenge for acid-demanding chemical treatments due to the buffering carbonate ions, expressed as equivalent mg CaCO₃/L (Lahay et al. 2007). Specifically, a substantial amount of acid is required to overcome high water alkalinity for the conventional Fenton process. BPA removal in synthetic solutions containing 0-200 mg CaCO₃/L water alkalinity were tested by the EFL platform. Results show that, solution of higher alkalinity was less prone to acidification by the Ella process, but the acidic zone was still below pH 4.14 in all tests under 100 mA electric current and 15 mL/min flow rate (FIG. 20C). This acidity led to an 84.5%-100% removal efficiency of BPA, significantly higher than that when electric current was turned off (FIG. 20D). The acidity produced by the Ella process could be tuned against water buffering capacity by adjusting applied electric current and hydraulic flow rate. For instance, a combination of 60 mA electric current and 2 mL/min flow rate is able to acidify a solution of 500 mg CaCO₃/L alkalinity from pH 8 to pH 3.5 (Yuan et al. 2013).

Example 3. Test with Field Water Samples

The results demonstrate the effectiveness of the EFL platform in synthetic solutions of complex water chemistry. Furthermore, in this study, water samples extracted in the field from surface or groundwater sources were used as the matrices for BPA removal with intrinsic conductivity supporting electrochemical water splitting. Water quality characteristics are shown in Table 2. Treated water bodies were acidified to pH 2.9-4.04 by the Ella process, and 91.7 to 97.2% BPA removals were achieved by the mediated Fenton-like process (FIG. 21 ).

Example 4. Techno-Economic Analysis

Compared with the conventional Fenton process, the required energy for electrochemical water splitting by this integral EFL platform is estimated to be 1.39 kWh/m³ influent, which translates into a cost of $0.091/m³ based on the average US industrial electricity rate ($0.0653/kWh) (Average Price of Electricity to Ultimate Customers by End-Use Sector, 2020). This value is subjected to optimization based on applied electric current, hydraulic flow rate, and solution conductivity, but it only constitutes around 10% of unit operating cost by modern water treatment plants (Guo et al. 2014). Besides, the cost of γ-Al₂O₃ and FeCl₃.6H₂O is estimated as $0.5/kg (Aluminum Oxide Price, 2020) and $0.3/kg (Ferric Chloride Price, 2020), respectively. This means it takes less than $0.0005 to synthesize 1 g of FeOCl/Al₂O₃ catalyst, and we used ˜50 g of synthesized catalyst particles for our device. By considering the long-term stability of this catalyst, its cost is indeed negligible. Furthermore, in situ electrochemical synthesis of highly concentrated H₂O₂ (Chen et al. 2017; Yamanaka et al. 2003) could be used as a replacement of externally supplied H₂O₂ in the future, further reducing the overall chemical cost.

Moreover, the EFL water treatment platform developed in this study is applied to practical implementation after upscaling. The fast response of the EFL platform in removing organic pollutants especially allows for smart controls at low cost. In addition, it possesses the easy-to-(un)install feature that makes it affordable and compatible with other connecting units of a centralized water treatment facility. For instance, a feasible niche of this device is to function as an electrochemical filter before advanced purification units requiring removal of fouling hazards such as organic molecules and biofilm-forming bacteria (Guo et al. 2011; Zhou et al. 1990). On the small size end, the EFL platform is designed to provide clean drinking water for individual families without electrical grid, by coupling with cheap photovoltaic sources.

DISCUSSION

An electro-Fenton-like (EFL) platform wherein an electrochemically produced acidic environment supports heterogeneous Fenton-like reaction was developed for high throughput water treatment of contaminated water. The acidic pH produced by the Ella process (100 mA electric current and 15 mL/min flow rate) mediated a 10.8-fold increase in HO. yield, which contributed to the complete removal of contaminants in the effluent. The EFL platform showed strong stability for long-term use, tolerance of high water flux, and effectiveness against complex water chemistry for organic contaminant removal. The setup configuration is advantageous in that it provides high degree of automation that enables water treatment by controlling the electric power, and low operating cost that most modern water treatment plants strive for, both of which are especially attractive for industrial applications.

The Ella process displays a small footprint because it turns neutral influent into acidic solution in between electrodes, and zones beyond that are neutral as the influent. Combined with heterogeneous Fenton-like catalysts, Ella process showed excellent performance under long-term use, high flow rate, and complex water chemistry, manifesting the robustness of this coupled platform for recalcitrant organic compounds removal.

REFERENCES CITED

-   Acar, Y. B., Alshawabkeh, A. N. Principles of electrokinetic     remediation. Environ. Sci. Technol. 27, 2638-2647 (1993). -   Adams, G. E., Boag, J. W. & Michael, B. D. Reactions of the hydroxyl     radical. Part 2.-Determination of absolute rate constants. Trans.     Faraday Soc. 61, 1417-1424 (1965). -   Aluminum Oxide Price [online], available from     <https://www.intratec.us/chemical-markets/aluminum-oxide-price>.     retrieved September 2020. -   André, R. et al. V₂O₅ nanowires with an intrinsic peroxidase-like     activity. Adv. Funct. Mater. 21, 501-509 (2011). -   Asati, A., Santra, S., Kaittanis, C., Nath, S. & Perez, J. M.     Oxidase-like activity of polymer-coated cerium oxide nanoparticles.     Angew. Chem. Int. Ed. 121, 2344-2348 (2009). -   Babuponnusami, A. & Muthukumar, K. A review on Fenton and     improvements to the Fenton process for wastewater treatment. J.     Environ. Chem. Eng. 2, 557-572 (2014). -   Bokare, A. D. & Choi, W. Review of iron-free Fenton-like systems for     activating H₂O₂ in advanced oxidation processes. J Hazard. Mater.     275, 121-135 (2014). -   Bolobajev, J. et al. Reuse of ferric sludge as an iron source for     the Fenton-based process in wastewater treatment. Chem. Eng. J. 255,     8-13 (2014). -   Brillas, E., Sirés, I. & Oturan, M. A. Electro-Fenton process and     related electrochemical technologies based on Fenton's reaction     chemistry. Chem. Rev. 109, 6570-6631 (2009). -   Cai, R. et al. Single nanoparticle to 3D supercage: framing for an     artificial enzyme system. J. Am. Chem. Soc. 137, 13957-13963 (2015). -   Cai, S. et al. Pt74Ag₂₆ nanoparticle-decorated ultrathin MoS₂     nanosheets as novel peroxidase mimics for highly selective     colorimetric detection of H₂O₂ and glucose. Nanoscale 8, 3685-3693     (2016). -   Cai, S. et al. Single-layer Rh nanosheets with ultrahigh     peroxidase-like activity for colorimetric biosensing. Nano Res. 11,     6304-6315 (2018). -   Chen, Z. et al. Development of a reactor with carbon catalysts for     modular-scale, low-cost electrochemical generation of H₂O₂ . React.     Chem. Eng. 2, 239-245 (2017). -   Chen, T. M., Wu, X. J., Wang, J. X. & Yang, G. W. WSe₂ few layers     with enzyme mimic activity for high-sensitive and high-selective     visual detection of glucose. Nanoscale 9, 11806-11813 (2017). -   Cheng, M. et al. Metal-organic frameworks for highly efficient     heterogeneous Fenton-like catalysis. Coord Chem. Rev. 368, 80-92     (2018). -   Clark, S. J. et al. First principles methods using CASTEP. Z.     Kristallogr Cryst. Mater. 220, 567-570 (2005). -   Davis, E. M. & Davis, R. J. Fundamentals of Chemical Reaction     Engineering. Journal of Chemical Education (Vol. 43, 2003). New     York, N: McGraw-Hill Higher Education. -   Deng, H. et al. Monodisperse magnetic single-crystal ferrite     microspheres. Angew. Chem. Int. Ed. 44, 2782-2785 (2005). -   De Smedt, F. & Wierenga, P. J. Solute transfer through columns of     glass beads. Water Resources Res. 20, 225-232 (1984). -   Ding, Y. et al. FePt—Au ternary metallic nanoparticles with the     enhanced peroxidase-like activity for ultrafast colorimetric     detection of H₂O₂ . Sensor. Actuat. B: Chem. 259, 775-783 (2018). -   Eggenhuisen, T. M., Breejen, J. P. D., Verdoes, D., Jongh, P. E. D.     & Jong, K. P. D. Fundamentals of melt infiltration for the     preparation of supported metal catalysts. The case of Co/SiO₂ for     Fischer-Tropsch synthesis. J. Am. Chem. Soc. 132, 18318-18325     (2010). -   Feng, F., Xu, Z., Li, X., You, W. & Zhen, Y. Advanced treatment of     dyeing wastewater towards reuse by the combined Fenton oxidation and     membrane bioreactor process. J. Environ. Sci. 22, 1657-1665 (2010). -   Ferric Chloride Price [online], available from     <https://www.icis.com/explore/resources/news/2001/08/27/145944/us-ferric-chloride-producers-raise-prices-in-healthy-market/>,     retrieved September 2020. -   Ganiyu, S. O., Van Hullebusch, E. D., Cretin, M., Esposito, G. &     Oturan, M. A. Coupling of membrane filtration and advanced oxidation     processes for removal of pharmaceutical residues: a critical review.     Sep. Purif. Technol. 156, 891-914 (2015). -   Ganiyu, S. O., Zhou, M. & Martinez-Huitle, C. A. Heterogeneous     electro-Fenton and photoelectro-Fenton processes: a critical review     of fundamental principles and application for water/wastewater     treatment. Appl. Catal., B. 235, 103-129 (2018). -   Garrido-Ramirez, E. G., Theng, B. K. G. & Mora, M. L. Clays and     oxide minerals as catalysts and nanocatalysts in Fenton-like     reactions—a review. Appl. Clay Sci. 47, 182-192 (2010). -   Gao, L. et al. Intrinsic peroxidase-like activity of ferromagnetic     nanoparticles. Nat. Nanotechnol. 2, 577-583 (2007). -   Gao, W. et al. Membrane fouling control in ultrafiltration     technology for drinking water production: a review. Desalination     272, 1-8 (2011). -   Gomes, H. I., Mayes, W. M., Rogerson, M., Stewart, D. I. &     Burke, I. T. Alkaline residues and the environment: a review of     impacts, management practices and opportunities. J. Clean. Prod.     112, 3571-3582 (2016). -   Guo, W., Ngo, H. H. & Li, J. A mini-review on membrane fouling.     Bioresour. Technol. 122, 27-34 (2012). -   Guo, T., Englehardt, J. & Wu, T. Review of cost versus scale: water     and wastewater treatment and reuse processes. Wat. Sci. Tech. 69,     223-234 (2014). -   He, Y et al. Microwave-Assisted Fabrication of Bimetallic PdCu     Nanocorals with Enhanced Peroxidase-Like Activity and Efficiency for     Thiocyanate Sensing. ACS Appl. Nano Mater. 1, 2397-2405 (2018). -   Herney-Ramirez, J., Vicente, M. A. & Madeira, L. M. Heterogeneous     photo-Fenton oxidation with pillared clay-based catalysts for     wastewater treatment: a review. Appl. Catal., B. 98, 10-26 (2010). -   Hojabri, S., Rajic, L. & Alshawabkeh, A. N. Transient reactive     transport model for physico-chemical transformation by     electrochemical reactive barriers. J. Hazard. Mater. 358, 171-177     (2018). -   Hu, L. et al. Copper nanoclusters as peroxidase mimetics and their     applications to H₂O₂ and glucose detection. Anal. Chico. Acta 762,     83-86 (2013). -   Jiang, T., Song, Y., Du, D., Liu, X. & Lin, Y. Detection of p₅₃     protein based on mesoporous Pt—Pd nanoparticles with enhanced     peroxidase-like catalysis. ACS Sensors 1, 717-724 (2016). -   Ji, X. X., Wang, H. F. & Hu, P. J. First principles study of Fenton     reaction catalyzed by FeOCl: reaction mechanism and location of     active site. Rare Metals 38, 783-792 (2019). -   Keith, D. C. et al. Geochemical models of the impact of acidic     groundwater and evaporative sulfate salts on Boulder Creek at Iron     Mountain, Calif. Appl. Geochem. 16, 947-961 (2001). -   Kim, M. C., Lee, D., Jeong, S. H., Lee, S. Y. & Kang, E.     Nanodiamond—Gold Nanocomposites with the Peroxidase-Like Oxidative     Catalytic Activity. ACS Appl. Mater. Interfaces 8, 34317-34326     (2016). -   Koppenol, W. H. The Haber-Weiss cycle-70 years later. Redox Rep. 6,     229-234 (2001). -   Lahav, O. & Birnhack, L. Quality criteria for desalinated water     following post-treatment. Desalination 207, 286-303 (2007). -   Lin, T. et al. Visual detection of blood glucose based on     peroxidase-like activity of WS₂ nanosheets. Biosens. Bioelectron.     62, 302-307 (2014). -   Lin, T., Zhong, L., Guo, L., Fu, F. & Chen, G. Seeing diabetes:     visual detection of glucose based on the intrinsic peroxidase-like     activity of MoS₂ nanosheets. Nanoscale 6, 11856-11862 (2014). -   Lin, L. et al. Intrinsic peroxidase-like catalytic activity of     nitrogen-doped graphene quantum dots and their application in the     colorimetric detection of H₂O₂ and glucose. Anal. Chico. Acta 869,     89-95 (2015). -   Liu, S., Lu, F., Xing, R. & Zhu, J. J. Structural effects of Fe₃O₄     nanocrystals on peroxidase-like activity. Chem.: Eur. J. 17, 620-625     (2011). -   Liu, Y, Zhu, G., Yang, J., Yuan, A. & Shen, X. Peroxidase-like     catalytic activity of Ag₃PO₄ nanocrystals prepared by a colloidal     route. PloS one 9, e109158 (2014). -   Liu, F. et al. Cu-hemin metal-organic frameworks with     peroxidase-like activity as peroxidase mimics for colorimetric     sensing of glucose. J. Nanopart. Res. 18, 106 (2016). -   Lu, L. et al. Wastewater treatment for carbon capture and     utilization. Nat. Sustain. 1, 750-758 (2018). -   Ma, M. et al. Size dependence of specific power absorption of Fe₃O₄     particles in AC magnetic field. J. Magn. Magn. Mater. 268, 33-39     (2004). -   Ma, M., Zhang, Y. & Gu, N. Peroxidase-like catalytic activity of     cubic Pt nanocrystals. Colloids Surf A 373, 6-10 (2011). -   Moon, G. H. et al. Eco-friendly photochemical production of H₂O₂     through O₂ reduction over carbon nitride frameworks incorporated     with multiple heteroelements. ACS Catal. 7, 2886-2895 (2017). -   Mu, J., Wang, Y., Zhao, M. & Zhang, L. Intrinsic peroxidase-like     activity and catalase-like activity of Co₃O₄ nanoparticles. Chem.     Comm. 48, 2540-2542 (2012). -   Mu, J., Li, J., Zhao, X., Yang, E. C. & Zhao, X. J. Novel     urchin-like Co₉S₈ nanomaterials with efficient intrinsic     peroxidase-like activity for colorimetric sensing of copper(II) ion.     Sensor. Actuat. B: Chem. 258, 32-41 (2018). -   Munoz, M., De Pedro, Z. M., Casas, J. A. & Rodriguez, J. J.     Preparation of magnetite-based catalysts and their application in     heterogeneous Fenton oxidation—a review. Appl. Catal., B. 176,     249-265 (2015). -   Nardi, A., Idiart, A., Trinchero, P., De Vries, L. M., &     Molinero, J. Interface COMSOL-PHREEQC (iCP), an efficient numerical     framework for the solution of coupled multiphysics and geochemistry.     Comput. Geosci. 69, 10-21 (2014). -   Neyens, E. & Baeyens, J. A review of classic Fenton's peroxidation     as an advanced oxidation technique. J. Hazard. Mater. 98, 33-50     (2003). -   Nordstrom, D. K. & Alpers, C. N. Negative pH, efflorescent     mineralogy, and consequences for environmental restoration at the     Iron Mountain Superfund site, California. Proc. Natl. Acad. Sci.     U.S.A. 96, 3455-3462 (1999). -   Parkhurst, D. L. & Appelo, C. A. J. PHREEQC (Version 3)—A Computer     Program for Speciation, Batch-Reaction, One-Dimensional Transport,     and Inverse Geochemical Calculations. In Modeling Techniques, book 6     (p. 497). (2013). -   Pariona, N., Herrera-Trejo, M., Oliva, J. & Martinez, A. I.     Peroxidase-like activity of ferrihydrite and hematite nanoparticles     for the degradation of methylene blue. J. Nanomater. 2016, U.S. Pat.     No. 3,427,809 (2016). -   Paz-Garcia, J. M., Villén-Guzman, M., Garcia-Rubio, A., Hall, S.,     Ristinmaa, M. & Cesar, G.-L. A Coupled Reactive-Transport Model for     Electrokinetic Remediation. In A. B. Ribeiro, E. P. Mateus, & N.     Couto (Eds.), Electrokinetics Across Disciplines and Continents (pp.     251-278). Cham: Springer International Publishing. (2016). -   Peng, Y. et al. Size- and shape-dependent peroxidase-like catalytic     activity of MnFe₂O₄ nanoparticles and their applications in highly     efficient colorimetric detection of target cancer cells. Dalton     Trans. 44, 12871-12877 (2015). -   Pignatello, J. J., Oliveros, E. & MacKay, A. Advanced oxidation     processes for organic contaminant destruction based on the Fenton     reaction and related chemistry. Crit. Rev. Environ. Sci. Technol.     36, 1-84 (2006). -   Pliego, G., Zazo, J. A., Blasco, S., Casas, J. A. & Rodriguez, J. J.     Treatment of highly polluted hazardous industrial wastewaters by     combined coagulation-adsorption and high-temperature Fenton     oxidation. Ind. Eng. Chem. Res. 51, 2888-2896 (2012). -   Pouran, S. R., Raman, A. A. A. & Daud, W. M. A. W. Review on the     application of modified iron oxides as heterogeneous catalysts in     Fenton reactions. J. Clean. Prod. 64, 24-35 (2014). -   Pouran, S. R., Aziz, A. A. & Daud, W. M. A. W. Review on the main     advances in photo-Fenton oxidation system for recalcitrant     wastewaters. J. Ind. Eng. Chem. 21, 53-69 (2015). -   Qin, F. X. et al. Hemin@metal-organic framework with peroxidase-like     activity and its application to glucose detection. Catal. Sci.     Technol. 3, 2761-2768 (2013). -   Qu, K., Shi, P., Ren, J. & Qu, X. Nanocomposite incorporating V₂O₅     nanowires and gold nanoparticles for mimicking an enzyme cascade     reaction and its application in the detection of biomolecules.     Chem.: Eur. J. 20, 7501-7506 (2014). -   Segall, M. D. et al. First-principles simulation: ideas,     illustrations and the CASTEP code. J. Phys.: Condens. Matter 14,     2717-2744 (2002). -   Smidsrød, O. & Skja, G. Alginate as immobilization matrix for cells.     Trends Biotechnol. 8, 71-78 (1990). -   Song, Y, Qu, K., Zhao, C., Ren, J. & Qu, X. Graphene oxide:     intrinsic peroxidase catalytic activity and its application to     glucose detection. Adv. Mater. 22, 2206-2210 (2010). -   Steefel, C. I. & Lasaga, A. C. A coupled model for transport of     multiple chemical species and kinetic precipitation/dissolution     reactions with application to reactive flow in single phase     hydrothermal systems. Am. J. Sci. 294, 529-592 (1994). -   Sun, C. et al. Fabrication of an inorganic-organic hybrid based on     an iron-substituted polyoxotungstate as a peroxidase for     colorimetric immunoassays of H₂O₂ and cancer cells. J. Mater. Chem.     A 1, 4699-4705 (2013). -   Sun, M. et al. Reinventing Fenton chemistry: iron oxychloride     nanosheet for pH-insensitive H₂O₂ activation. Environ. Sci. Tech.     Let. 5, 186-191 (2018). -   Thomas, N. et al. Heterogeneous Fenton catalysts: A review of recent     advances. Journal of Hazardous Materials 404, 124082 (2021). -   US Average Price of Electricity to Ultimate Customers by End-Use     Sector [online], <.     https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a>,     retrieved April 2020. -   Vandenberg, L. N., Hauser, R., Marcus, M., Olea, N. &     Welshons, W. V. Human exposure to bisphenol A (BPA). Reproductive     Toxicol. 24, 139-177 (2007). -   Versteeg, H. K. & Malalasekera, W., 2007. An introduction to     computational fluid dynamics: the finite volume method. Pearson     education. -   Wang, J., Han, D., Wang, X., Qi, B. & Zhao, M. Polyoxometalates as     peroxidase mimetics and their applications in H₂O₂ and glucose     detection. Biosens. Bioelectron. 36, 18-21 (2012). -   Wang, Q. et al. The peroxidase-like catalytic activity of ferrocene     and its application in the biomimetic synthesis of microsphere     polyaniline. New J. Chem. 42, 13536-13540 (2018). -   Wang, S., Xu D. et al. Ultrathin ZIF-67 nanosheets as a colorimetric     biosensing platform for peroxidase-like catalysis. Anal. Bioanal.     Chem. 410, 7145-7152 (2018). -   Wang, C., Gao, J. & Tan, H. Integrated Antibody with Catalytic     Metal-Organic Framework for Colorimetric Immunoassay. ACS Appl.     Mater. Interfaces 10, 25113-25120 (2018). -   Wardman, P. Reduction Potentials of One-Electron Couples Involving     Free Radicals in Aqueous Solution J. Phys. Chem. Ref. Data 18,     1637-1755 (1989). -   Wu, Y. et al. Transformation of pollutants in landfill leachate     treated by a combined sequence batch reactor, coagulation, Fenton     oxidation and biological aerated filter technology. Process Saf     Environ. 89, 112-120 (2011). -   Wu, X., Chen, T., Wang, J. & Yang, G. Few-layered MoSe₂ nanosheets     as an efficient peroxidase nanozyme for highly sensitive     colorimetric detection of H₂O₂ and xanthine. J. Mater. Chem. B 6,     105-111 (2018). -   Yamanaka, I., Onizawa, T., Takenaka, S. & Otsuka, K. Direct and     continuous production of hydrogen peroxide with 93% selectivity     using a fuel-cell system. Angew Chem. Int. Ed. 42, 3653-3655 (2003). -   Yang, X. J., Xu, X. M., Xu, J. & Han, Y F. Iron oxychloride (FeOCl):     an efficient Fenton-like catalyst for producing hydroxyl radicals in     degradation of organic contaminants. J. Am. Chem. Soc. 135,     16058-16061 (2013). -   Ye, H. et al. Peroxidase-like properties of Ruthenium nanoframes.     Sci. Bull. 61, 1739-1745 (2016). -   Yi, Y, Wang, L., Li, G. & Guo, H. A review on research progress in     the direct synthesis of hydrogen peroxide from hydrogen and oxygen:     noble-metal catalytic method, fuel-cell method and plasma method.     Catal. Sci. Technol. 6, 1593-1610 (2016). -   Yuan, S., Chen, M., Mao, X. & Alshawabkeh, A. N. A three-electrode     column for Pd-catalytic oxidation of TCE in groundwater with     automatic pH-regulation and resistance to reduced sulfur compound     foiling. Water Res. 47, 269-278 (2013). -   Zeb, A. et al. Intrinsic peroxidase-like activity and enhanced     photo-Fenton reactivity of iron-substituted polyoxometallate     nanostructures. Dalton Trans. 47, 7344-7352 (2018). -   Zhang, X. Z., Zhou, Y, Zhang, W., Zhang, Y. & Gu, N.     Polystyrene@Au@prussian blue nanocomposites with enzyme-like     activity and their application in glucose detection. Colloids Surf A     490, 291-299 (2016). -   Zheng, H. Q. et al. MOF-808: A Metal-Organic Framework with     Intrinsic Peroxidase-Like Catalytic Activity at Neutral pH for     Colorimetric Biosensing. Inorg. Chem. 57, 9096-9104 (2018). -   Zhou, X. & Mopper, K. Determination of photochemically produced     hydroxyl radicals in seawater and freshwater. Mar. Chem. 30, 71-88     (1990).

INCORPORATION BY REFERENCE

All of the U.S. patents and U.S. and PCT published patent applications cited herein are hereby incorporated by reference.

EQUIVALENTS

The foregoing written specification is considered to be sufficient to enable one skilled in the art to practice the invention. The present invention is not to be limited in scope by examples provided, since the examples are intended as a single illustration of one aspect of the invention and other functionally equivalent embodiments are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and fall within the scope of the appended claims. The advantages and objects of the invention are not necessarily encompassed by each embodiment of the invention. 

What is claimed is:
 1. A process for treating contaminated water, comprising contacting said contaminated water with hydrogen peroxide in the presence of an iron oxychloride catalyst, and subsequently applying an electric current to the contaminated water, wherein the process occurs in the absence of an additional acid, and the iron oxychloride catalyst is a FeOCl/Al₂O₃ composite.
 2. The process of claim 1, wherein the electric current is about 100 mA.
 3. The process of claim 1, wherein the contaminated water subjected to the electric current attains a pH of about 2 to about
 4. 4. The process of claim 1, wherein the iron oxychloride catalyst is immobilized on a support.
 5. The process of claim 4, wherein the iron oxychloride catalyst is immobilized on a γ-Al₂O₃ support.
 6. The process of claim 1, wherein the amount of one or more organic contaminants in the water is decreased.
 7. The process of claim 6, wherein the one or more contaminants is one or more drugs, drug precursors, plastic precursors, herbicides, pesticides, or recalcitrant dyes.
 8. The process of claim 7, wherein the one or more contaminants is bisphenol A (BPA).
 9. A process for treating contaminated water, comprising: (i) adding hydrogen peroxide to the contaminated water; (ii) providing an influent stream of the contaminated water at a flow rate into a chamber comprising an upstream anode, a downstream cathode, and an iron oxychloride catalyst between the anode and cathode; (iii) applying an electric current to the chamber to provide an acidic environment in the chamber, thereby treating the contaminated water in the chamber; and (iv) collecting an effluent stream of the treated water exiting the chamber; wherein the iron oxychloride catalyst is a FeOCl/Al₂O₃ composite.
 10. The process of claim 9, wherein the influent stream of contaminated water is at about neutral pH; and effluent stream of treated water is at about neutral pH.
 11. The process of claim 9, wherein the contaminated water in the chamber is at an acidic pH.
 12. The process of claim 11, wherein the pH of the contaminated water in the chamber is about 2 to about
 4. 13. The process of claim 9, wherein the electric current is about 100 mA.
 14. The process of claim 9, wherein the iron oxychloride catalyst is immobilized on a γ-Al₂O₃ support.
 15. The process of claim 9, wherein the hydrogen peroxide is converted to hydroxy radicals inside the chamber.
 16. The process of claim 15, wherein the concentration of hydroxy radicals in the chamber during step (iii) is greater than 250 μM.
 17. The process of claim 9, wherein the flow rate is about 10 to about 25 mL/min.
 18. The process of claim 9, wherein the amount of one or more organic contaminants in the water is decreased, and the one or more contaminants is one or more drugs, drug precursors, plastic precursors, herbicides, pesticides, or recalcitrant dyes.
 19. The process of claim 18, wherein the one or more contaminants is bisphenol A (BPA).
 20. A process for treating contaminated water, comprising contacting said contaminated water with hydrogen peroxide in the presence of an iron oxychloride catalyst, and subsequently applying an electric current to the contaminated water, wherein the process occurs in the absence of an additional acid; and the electric current is about 100 mA or the concentration of hydroxy radicals in the contaminated water while applying the electric current is greater than 250 μM.
 21. A process for treating contaminated water, comprising: (i) adding hydrogen peroxide to the contaminated water; (ii) providing an influent stream of the contaminated water at a flow rate into a chamber comprising an upstream anode, a downstream cathode, and an iron oxychloride catalyst between the anode and cathode; (iii) applying an electric current to the chamber to provide an acidic environment in the chamber, thereby treating the contaminated water in the chamber; and (iv) collecting an effluent stream of the treated water exiting the chamber; wherein the electric current is about 100 mA or the concentration of hydroxy radicals in the chamber during step (iii) is greater than 250 μM. 